1. Field of the Invention
The present invention relates to a semiconductor electron emitting device and, more particularly, to a semiconductor electron emitting device in which an avalanche amplification is caused and electrons are changed to hot electrons and then emitted.
2. Related Background Art
Hitherto, among semiconductor electron emitting devices, there have been known devices using the avalanche amplification as disclosed in U.S. Pat. Nos. 4,259,678 and 4,303,930. Such devices are constructed in the following manner. A p type semiconductor layer and an n type semiconductor layer are formed so as to be come into contact with each other, thereby forming a diode structure. By applying a reverse bias voltage between both electrodes of the diode, the avalanche amplification is caused and the electrons are changed to the hot electrons. The electrons are emitted from the surface of the n type semiconductor layer in which a work function is reduced by depositing cesium or the like onto the surface of the n type semiconductor layer.
In the above conventional devices, to reduce the work function of the electron emitting section, cesium and cesium-oxygen compound are formed on the surface of the electron emitting section. However, since the cesium material is chemically extremely active, there are problems such that (1) the stable operation is performed only when the cesium material is used at a super high vacuum (to 10.sup.-7 Torr or more), (2) the life changes depending on a degree of vacuum, (3) the efficiency changes depending on a degree of vacuum, (4) and the like. On the other hand, the hot electrons generated at the pn interface are dispersed and lose the energy when they pass through the n type semiconductor layer. Therefore, it is necessary to very thinnly form the n type semiconductor layer (for instance, 200 .ANG. or less). However, many problems on the semiconductor manufacturing process exist in the case of uniformly forming such an extremely thin n type semiconductor layer at a high concentration and less defect. It is difficult to stably manufacture the device.